The administration will use Obama's fearsome campaign infrastructure to try to galvanize backers around an issue that faces a protracted fight on Capitol Hill.

Vice President Joe Biden, speaking to the U.S. Conference of Mayors on gun… (Manuel Balce Ceneta, Associated…)

WASHINGTON — A day after President Obama announced a wide-ranging series of gun-control initiatives, the administration kicked off its campaign to create public support and pressure lawmakers to pass the most comprehensive legislation since the mid-1990s.

"We're going to take this fight to the halls of Congress. We're going to take it beyond that," Vice President Joe Biden told the U.S. Conference of Mayors on Thursday. "We're going to take it to the American people. We're going to go around the country making our case, and we're going to let the voice of the American people be heard."

The administration will use Obama's fearsome campaign infrastructure to try to galvanize supporters around an issue that faces a protracted fight on Capitol Hill. To do so, the administration will pit its own grass-roots network against gun-rights groups, such as the National Rifle Assn.

"If you think we've suffered too much pain to allow this to continue, put down the paper, turn off the computer, and get your members of Congress on record," Obama wrote in an opinion piece in the Connecticut Post. "Ask them why getting an A-grade from the gun lobby is more important than giving parents some peace of mind when they drop their child off for first grade."

The newspaper is based in Bridgeport, near Newtown, the site of last month's school shooting that left 20 children and six staff members dead and set off calls for new gun laws.

The mobilization efforts by the president's campaign committee began in earnest Thursday, with campaign manager Jim Messina emailing supporters an online petition and urging them to "stand with the president."

Biden, in his speech to the mayors, acknowledged that there may not be "absolute unanimity" on how to mitigate gun violence, but emphasized consensus.

"Everyone acknowledges we have to do something.... I hope we all agree that mass shootings like the ones that we witnessed in Newtown 34 days ago cannot continue to be tolerated," he said.

Biden outlined many of the initiatives announced by Obama on Wednesday, including administrative actions to improve federal research on gun-related violence and to direct the attorney general to reevaluate the categories of people who should be prohibited from owning a gun. And he made a forceful pitch for the policies that must pass Congress, including a universal background-check system for every gun sale and a ban on high-capacity magazines.

"High-capacity magazines don't have a practical sporting purpose or hunting purpose. As one hunter told me, if you got 12 rounds, it means you've already missed the deer 11 times," Biden said. "You should pack the sucker in at that point."

But Biden spent much less time speaking about an assault weapons ban, which will face stiff opposition in Congress. He also contended that the gun industry would exploit any loopholes in a new law to continue to manufacture the weapons.

"I know as well as anyone, having written the first assault weapons ban, that the industry will do whatever it can to get around it, and they'll figure out a way," the vice president said. "But I also know we have to try."

Chris Koos, the mayor of Normal, Ill., said a "surprising" number of his constituents have voiced support for an assault weapons ban. "I thought there'd be some push-back," Koos said, in his city of 52,000 people in a rural region. But he said Vietnam veterans have been particularly outspoken in their support for a ban, having used similar firearms in combat.

"They know what they are for," Koos said.

But Betsy Price, mayor of Fort Worth, Texas, said most residents of her city were opposed to bans on assault weapons or high-capacity magazines.

But Price praised the president's efforts to improve mental health treatment and record-keeping, especially the executive action informing healthcare providers that they are not prevented from sharing relevant information about people who are prohibited from owning guns for mental health reasons.

Biden took pains to assert that the White House respected the 2nd Amendment.

Omaha Mayor Jim Suttle said that message may resonate in his state. "Nebraska is certainly a very, very conservative state. A red state, solid. But when you start polling people, particularly my constituents, you start seeing there is a public concern about the gun violence," he said.

"That's what the vice president is trying to do," Suttle said. "He's saying, 'Hey, the 2nd Amendment is your right. It's our right. Let's move on to the other aspects.'"

Dick Moore, the mayor of Elkhart, Ind., said Biden's choice for his first day on the stump was a savvy one. "He just sent a whole bunch of emissaries back home with what he said," Moore said. "Whether you're for or you're against, you get the word around the country pretty fast this way."